In order to better understand the molecular mechanism of Ca2 ion transport and regulation in muscle, the information contained in the primary structure of the Ca2 ion binding proteins of the sarcoplasmic reticulum membrane and contractile apparatus will be extracted. The amino acid sequences of the following proteins will be determined: ATPase protein from the sarcoplasmic reticulum of rabbit skeletal muscle, troponin C from lobster fast skeletal muscle, a troponin C-like Ca2 ion-binding protein from scallop striated muscle, and myosin light chains from human blood platelets. The sequences of these and other related proteins, and the methods used to determine them, will be used to design and carry out chemical modification studies aimed at directly locating functionally critical parts of the molecules. Information from the sarcoplasmic reticulum ATPase will be examined for clues to the chemical nature of the protein-Ca2-phospholipid interactions involved in Ca2 ion uptake and release by the membrane, and will provide a frame of reference for comparison with cardiac muscle sarcoplasmic reticulum and other cation-transporting membrane ATPases. Comparative studies on troponin C and the related myosin light chains are designed to identify the structural alterations that have led to functional divergence to locate functionally important amino acid residues, and to examine the similarities and differences between the two types (myosin-linked and troponin-linked) of intracellular Ca ion regulatory systems. The relationship between membrane and contractile proteins will be evaluated by comparing the sequence of the sarcoplasmic reticulum ATPase protein with the known sequences of other proteins that bind ATP and participate in energy transduction (e.g., other membrane ATPases, myosin heavy chains, actin, tubulin).